Metathesis catalysts have been previously described by for example, U.S. Pat. Nos. 5,312,940, 5,342,909, 5,728,917, 5,750,815, 5,710,298, and 5,831,108 and PCT Publications WO 97/20865 and WO 97/29135 which are all incorporated herein by reference. These publications describe well-defined single component ruthenium or osmium catalysts that possess several advantageous properties. For example, these catalysts are tolerant to a variety of functional groups and are more active than previously known metathesis catalysts. Olefin metathesis is a carbon-carbon bond breaking/bond making process in which there is an overall exchange of double bond moieties between two olefins. The. three main ways that olefin metathesis can be applied are illustrated in Scheme 1. Ring-opening metathesis polymerization (ROMP) involves the formation of polyolefins from strained cyclic olefins; ring-closing metathesis (RCM) involves the intramolecular transformation of an alpha, omega-diene to a cyclic olefin; and acyclic diene metathesis (ADMET) involves the intermolecular exchange of olefins. 
Olefin metathesis can be mediated by a number of transition metals, but the two most widely used catalysts are the Schrock molybdenum alkylidene (1) and the Grubbs ruthenium alkylidene (2). FIGS. 1A and 1B show examples of these two catalysts.
The commercial availability and high activity of these well-defined, single-component catalysts has led to the development of olefin metathesis as a standard synthetic method. In particular, RCM has been applied to a diverse array of problems, ranging from the total synthesis of natural products to the synthesis of catenanes. As one review author recently commented, ring-closing metathesis xe2x80x9chas come of age as a synthetic technique. It is no longer a novelty, to be included in the title of every paper, it is a synthetic tool available to every practicing organic synthetic chemist.xe2x80x9d
Yet, there is still considerable room for improvement. Neither 1 nor 2 is a xe2x80x9cperfectxe2x80x9d catalyst; each has significant problems associated with it. Although the Schrock alkylidene (1) has the greater overall activity, it suffers from extreme air and moisture sensitivity, and it lacks tolerance for many functional groups (e.g. alcohols, aldehydes, and carboxylic acids). On the other hand, the Grubbs alkylidene (2) is easier and less expensive to make, is air stable as a solid and has a much wider functional group tolerance, but its activity is limited to at least two orders of magnitude less than 1. Additionally, neither 1 nor 2 provides stereo-selective control over the metathesis products.
Because of these problems, the design of metathesis catalysts with better activity, stability, and selectivity is an area of active investigation. Recently, several modifications of complex 2 have been reported, including a heterobimetallic complex (3), a bidentate Schiff base supported complex (4), and a bis (N-heterocyclic carbene) substituted complex (5). FIGS. 2A, 2B and 2C show examples of each of these liganids.
Complex 3 is approximately 80 times more active than 2 for the ROMP of 1,5-cyclooctadiene, and so it can be used as an alternative in RCM reactions that would proceed too slowly with 2 to be practical. However, at the same time, 3 is also more unstable than 2 and decomposes more rapidly. Complex 4 is more active at elevated temperatures than 2 for RCM, and it has the advantage of remaining active in polar protic media. Finally, complex 5 displays ROMP and RCM activity at elevated temperatures that is comparable to the activity of 2 at room temperature.
Thus, there is a need for a stable, more active metathesis catalyst. The invention address this need by providing for mono-substituted derivatives as more active metathesis catalysts than those previously examined. In addition, the invention provides a method of attaching N-heterocyclic carbene ligands to a metal center and methods of using the same.